Gas analyzing apparatus

ABSTRACT

A gas analyzer comprising a pump unit and autocalibration means, characterized in that the gas analyzer is connected to a storage tank having a calibrated leak and filled with a mixture of n gases having different masses, and wherein the partial leakage flow of each of said n gases which through said calibrated leak is known.

BACKGROUND OF THE INVENTION

The invention concerns a gas analyser including a pump unit andautocalibration means.

The invention applies in particular to a gas analyser that is part of atracer gas leak detector.

Tracer gas leak detectors generally include autocalibration means, i.e.means for calibrating the detector. To this end the device includes acontainer of tracer gas, generally helium, having a known and calibratedleakage rate.

The container is connected to the inlet of the detector by a valve whichis opened during autocalibration. To enable calibration, the calibratedleakage flow is entered into an electronic circuit, for example usingthumbwheels on the device, the electronic circuit adjusting theionisation current of the gas analyser. The device carries a massselector switch, generally selecting one of three separate possiblemasses, operating on the ion acceleration voltage. This is so eventhough the detector contains only one calibrated leakage container for agiven gas.

Accordingly, if a tracer gas other than that in the calibrated leakagecontainer inside the device is to be used, it is necessary to use acalibrated leakage cylinder of the other gas and to connect it to theinlet flange of the device and of course to open the device to set thecalibrated leakage value of that cylinder on the thumbwheels. The massselector switch must also be set to the position corresponding to thegas used.

When this has been done, the above parameters (ion acceleration voltageand ionisation current) are adjusted automatically duringautocalibration so that the leak shown on the device corresponds to thecalibrated leakage flow entered via the thumbwheels.

SUMMARY OF THE INVENTION

An aim of the present invention is therefore to propose a gas analyserequipped with means for automatically calibrating it in a very simplemanner using a plurality of different gases.

An analyser of the above kind can be used directly to analyse a gas oras part of a leak detector that can be used with a plurality ofdifferent tracer gases by simplifying to the greatest possible degreethe operations to be carried out when the tracer gas used is changed.

The invention therefore consists in a gas analyzer connected to a pumpunit and including auto calibration means characterised in that it isconnected to a storage tank having a calibrated leak and filled with amixture of n gases having different masses and the leakage flow of eachof said n gases which through said calibrated leak is known.

In an advantageous embodiment of the invention, the concentration ofeach of the n gases in the mixture is such that said partial leakageflow of each of the n gases through said calibrated leak is the same forall of them. This enables a single value of the leakage flow to be setthat is valid for all the n gases.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of the invention will now be described with reference tothe accompanying drawings, in which:

FIG. 1 is a diagram of a tracer gas leak detector including a gasanalyser in accordance with the invention, and

FIG. 2 is a diagram of a gas analyser in accordance with the inventionused directly to analyse a flow of gas.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a tracer gas leak detector using a gas analyser inaccordance with the invention. The gas analyser, within the dashed lineframe 1, comprises a mass spectrometer 2 with its pump unit, comprisinga secondary pump 3 and a primary pump 4, and autocalibration means.

The autocalibration means include a storage tank 6 having a calibratedleak (for example a calibrated orifice). The storage tank is connectedto the spectrometer 2 by a pipe 5 via a valve 7 controlled by anelectronic automatic control circuit 8.

In accordance with the invention, the storage tank 6 is filled with amixture of n gases with different masses (for example helium 4, helium3, and hydrogen). The partial leakage flow of each of the n gasesthrough the calibrated leak is obviously known.

The concentration of each of the n gases in the mixture is preferablychosen so that its partial leakage flow is identical to that of each ofthe other gases in the mixture. The autocalibration means furtherinclude an electronic circuit 9 which to select the mass operates on thevoltage accelerating ions formed in the mass spectrometer 2. Theelectronic circuit is controlled by a mass selector button 10. Finally,an electronic circuit 11 operates on the electronic current emitted bythe cathode (filament or cold cathode) of the spectrometer to adjust theionisation current (sensitivity adjustment). The parameters of thiselectronic circuit are varied by thumbwheels 12 on which the partialleakage flow of each of the gases in storage tank 6 is set (a singlevalue is sufficient because the concentration of each gas is chosen sothat its partial leakage flow is the same as that of the other gases).

To enable use of the leak detector, a valve 13 is disposed between theprimary pump 4 and the secondary pump 3 and an inlet flange 14 adaptedto be connected to an enclosure to be tested is connected to a primarypump 4 by a pipe 15 equipped with a pre-drain valve 16 and on the otherhand to the spectrometer 2 via a pipe 17 equipped with an inlet valve18.

With a device of the above kind, if the tracer gas is changed, it issufficient to set the mass of the gas used on the button 10 duringcalibration.

If the leakage flow of each gas is not the same, the value of theleakage flow must also be modified on the thumbwheels 12. This is why itis preferable to choose for each gas in the storage tank 6 aconcentration such that the partial leakage is the same for each gas.

With a device of the above kind, only one storage tank 6 is needed.

In FIG. 2, the gas analyser is used directly to analyse a gas mixture bymass spectrometry. The mixture is fed in at 19.

Here the storage tank 6 is therefore used to calibrate the analyser foreach of the n gases that it contains using the known leakage value foreach gas: as previously, an identical partial leakage is chosen for eachgas by choosing suitable concentrations. In this application, theelectronic circuit 9 includes a memory and the button 10 is replaced bya cyclic switch 20 scanning the masses of the gases contained in thestorage tank 6. During calibration, the valve 7 is open and the settingof, the acceleration voltage corresponding to each mass is stored in thememory of the circuit 9. When analyzing a gas fed in at 19, with valve 7closed, the switch 20 scans all the masses in succession and for eachmass the circuit 9 sets the value of the acceleration voltage stored inmemory for each mass during calibration.

What is claimed is:
 1. A gas analyser comprising: a pump unit; and anautocalibrator, wherein said gas analyser is connected to a storage tankhaving a calibrated leak and filled with a mixture of n gases havingdifferent masses, and a partial leakage flow of each of said n gaseswhich through said calibrated leak is known.
 2. The gas analyseraccording to claim 1, wherein the concentration of each of the n gasesin the mixture is such that said partial leakage flow of each of the ngases through said calibrated leak is the same.
 3. The gas analyseraccording to claim 1, wherein said gas analyser is part of a leakdetector.
 4. The gas analyser of claim 1, wherein said pump unitcomprises a primary pump and a secondary pump.
 5. The gas analyser ofclaim 4, further comprising: a valve connecting said primary pump andsaid secondary pump; and an inlet flange coupled to the primary pump viaa pipe equipped with a pre-drain valve, said inlet flange also coupledto a spectrometer.
 6. The gas analyser of claim 1, said autocalibratorcomprising: a first electronic circuit, controlled by a mass selector,that selects the mass, said electronic circuit operating on voltageaccelerating ions; and a second electronic circuit that operates oncurrent emitted by a cathode to provide sensitivity adjustment.
 7. Thegas analyser of claim 6, wherein parameters of said second circuit arecontrolled by a thumbwheel.
 8. The gas analyser of claim 1, furthercomprising: a memory in an electronic circuit that sets a value of theacceleration voltage for each of said n gases; and a cyclic switch thatsuccessively scans the masses of gases in said storage tank.